The present invention relates to a high-tenacity water-soluble polyvinyl alcohol (hereinafter abbreviated to "PVA") fiber and a process for producing the same. More particularly, this invention is concerned with a novel water-soluble PVA fiber not only having excellent mechanical properties comparable to those of an aramid fiber but also exhibiting very high dissolving shrinkage ratio and dissolving shrinkage stress, as opposed to the conventional water-soluble PVA fiber.
Examples of the water-soluble fibers well known to the art which is soluble in hot water or water of room temperature include a PVA fiber, an alginate fiber, a cellulose fiber, and a polyethylene oxide fiber. However, among them, only PVA fiber can meet the requirements with respect to the mechanical properties for further processing such as spinning and knitting and weaving, while the other fibers cannot meet the requirements with respect to the mechanical properties. Examples of the process for producing the above-described PVA fiber include one wherein an aqueous high concentration solution of PVA having a degree of saponification as low as 99 mol % is dry-spun (Japanese Patent Publication No. 892/1968) and one wherein the acetalization is not conducted after wet-spinning of an aqueous solution of completely saponified PVA having a degree of saponification of 99 mol % into a saturated aqueous solution of Glauber's salt.
However, the tensile strength and the initial modulus of the water-soluble PVA fibers prepared by the above-described processes are as low as about 3 to 4 g/d and about 50 to 60 g/d, respectively. Although the dissolution of the above-described fibers in water is accompanied with shrinkage, the maximum dissolving shrinkage ratio and the maximum dissolving shrinkage stress are as low as about 50% and about 200 mg/d, respectively. For this reason, the above-described fibers have been used only for special applications such as backing fabrics for chemical laces and raveling cords for socks, and it has been impossible to find applications in the industries where high mechanical properties are required.
In recent years, industrial materials which maintain the shape with predetermined mechanical properties for a given period but disappear through self-disintegration after passage of the given period have been desired in the art. That is, underwater disintegrable high tenacity fiber materials and high tenacity ropes have been desired in the art.
However, it was quite impossible to apply the above-described conventional fibers to these special applications.